As an optical recording medium as described above, an optical disk (the so-called CD-R disk) of "write-once" type is practically available into which a user can write (or record) data only once. This optical recording medium Attachment A includes a recording film made of a pigment material, for example, an organic pigment material such as a cyanine based compound, a phthalocyanine based compound and so on.
In order to form the recording film on a substrate in the production of the optical disk as described above, a spin coating method is generally employed in which a pigment material is dissolved in a solvent to obtain a solution, which is applied onto the substrate by means of a spin coater and dried.
The recording film formed as described above generally has a thickness of 0.1 to 0.3 .mu.m, and uniformity of thickness over the entire surface of the substrate is required. In order to meet this requirement, various measures are proposed such as developments of techniques for applying the pigment material including selection of solvents and precise control of a rotating table of the spin coater as well as thorough management of a surrounding atmosphere for performing the coating process and surface conditions of the substrate.
However, with the spin coating method as mentioned above, it is not easy to control thickness variation of the recording film among individual disks and/or thickness variation of the recording film within a single disk within a given degree by means of the conventional technique for forming the recording film or the management of the surrounding atmosphere for forming the recording film as described above when the thickness of the recording film to be formed is smaller, for example, near 0.1 .mu.m.
Also, the spin coating method has an inherent problem that the thickness of the recording film changes along a radial direction of the disk, namely that the thickness of the recording film to be formed tends to be larger on an outer peripheral side than on an inner peripheral side of the disk. This renders it extremely difficult to stably form a recording film having a thickness which is uniform among individual disks or within a single disk.
Further, instead of the above-mentioned spin coating method, there is known a method of producing the optical recording medium characterized by forming the recording film on the substrate by means of a vacuum deposition method which is one of the so-called dry processes. It is expected that this method would improve the uniformity of the thickness of the recording film to be formed. However, this method involves other problems such as low productivity and dust adhesion. Therefore, in order to efficiently perform the vacuum deposition method, it is desired that these problems are at least suppressed or preferably substantially solved.